The present invention relates to substrates provided with a coating possessing a photocatalytic property based on titanium dioxide, the said titanium dioxide being partly incorporated in the form of particles. It also relates to a process for the preparation of these substrates and of novel organic dispersions based on monodisperse titanium dioxide particles which can be used in this process.
It is known to functionalize materials for various applications, such as materials for vehicles or for buildings (glass, metals, ceramics, facing, cladding or roofing materials, such as tiles, and the like), by conferring on them properties such as, in particular, anti-UV, dirt-repellent, bactericidal, anti-glare, anti-static or antimicrobial properties and the like.
This is particularly true in the case of glazing, such as windscreen glazing for transportation means, where attempts have been made to functionalize them by depositing, at the surface thereof, thin layers intended to confer thereon a specific property according to the targeted application.
Thus, there exist layers with an optical function, such as so-called anti-glare layers composed of a stack of layers alternatively with high and low refractive indices. For an anti-static function or a heating function of the anti-icer type, it is also possible to provide electrically conductive thin layers, for example based on metal or doped metal oxide. For an anti-solar or low-emissivity thermal function, for example, thin layers made of metal of the silver type or based on metal oxide or nitride may be used. To obtain a xe2x80x9crain-repellentxe2x80x9d effect, it is possible to provide layers with a hydrophobic nature, for example based on fluorinated organosilane, and the like.
Currently, another desired property is to obtain the permanence over time of the appearance and surface properties, which makes it possible in particular to render cleaning less frequent and/or to improve the visibility, by succeeding in removing, as they are formed, the dirty marks which are gradually deposited at the surface of the substrate, in particular dirty marks of organic origin, such as finger marks or volatile organic products present in the atmosphere, or even dirty marks of condensation type.
A solution to these problems of dirty marks consists, for example, in depositing on the substrates a coating which provides for degradation of these dirty marks by photocatalysis. Under the effect of radiation of appropriate wavelength, the components of the coating initiate radical reactions which cause oxidation of organic products.
This degradation can be induced by any compound which generates radicals under the effect of light (photocatalytic effect). It can relate in particular to titanium dioxide, which is already employed for the treatment of architectural substrates and in particular glass substrates.
Thus, it is known to use solutions of titanium compounds or colloidal titanium dioxide dispersions to create photocatalytic properties on the substrates. However, it has been found that the specific characteristics of the said solutions of titanium compounds or colloidal titanium dioxide dispersions used to treat the substrate influence the quality of the photocatalytic coating. Depending on the specific characteristics, the quality of the adhesion of the coating to the substrate can also be highly variable. Finally, it happens, in the case where the substrate is of glass, that the coating causes a lack of transparency and a fuzziness on the glass.
One aim of the present invention is thus to provide novel substrates possessing a coating based on titanium dioxide exhibiting good photocatalytic properties, the said coatings being durable, transparent and capable of being prepared industrially.
With this aim, the invention relates to a substrate provided, on at least a portion of one of its faces, with a coating with a photocatalytic property based on titanium dioxide which is at least partially crystalline and which is incorporated in the said coating partly in the form of particles predominantly crystallized in the anatase form.
The invention also relates to processes for producing this substrate, which consists in depositing the coating by liquid-phase pyrolysis or by a so-called sol-gel technique from a suspension comprising at least one organometallic compound and a dispersion of titanium dioxide particles, the said particles exhibiting the characteristics of the particles incorporated in the final coating.
Finally, the invention relates to an organic dispersion comprising:
titanium dioxide particles with a size of between 5 and 70 nm which are monodisperse and predominantly in the anatase crystalline form,
and at least one organic solvent, preferably exhibiting a latent heat of vaporization which is less than that of water. This dispersion is used for the preparation of the substrate according to the invention.